Method and apparatus for mixing two gases in a predetermined proportion

ABSTRACT

A method for the control of the proportion of two gases which are delivered to a mixed gas line for use for example in a respiratory breathing apparatus in which the gases are delivered to a mixed gas line from a pressure control vessel, comprises continuously monitoring the pressure in the control vessel and when the pressure therein is at an initial predetermined pressure admitting a first gas into the pressure control vessel until the pressure therein increases to a predetermined higher pressure and then stopping the admission of the first gas and initiating the admitting of a second gas into the pressure control vessel, continuing to admit the second gas until a predetermined additional higher pressure is achieved in the pressure control vessel, discontinuing the admission of the second gas when the predetermined additional higher pressure is reached and initiating the withdrawal of the mixed gas through the mixed gas line, continuing to withdraw the mixed gas through the mixed gas line until an initial pressure is again reached in the pressure control vessel at which time the complete process is repeated again. The apparatus includes a first control valve in a first gas supply line to the pressure vessel and a second control valve in a second gas supply line to the pressure control vessel. A third control valve is arranged in a mixed gas delivery line which connects the pressure vessel. All of the three valves are connected by a control device which is responsive to the pressure in the pressure vessel and the individual control valves are set for opening and closing at different control pressures so that the inflow of the first and second gases and the delivery of the mixed gases will be continuously controlled thereby.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to a method and apparatus for mixingtwo gases in a predetermined proportion and in particular to a new anduseful apparatus and method for continuously supplying a gas mixturefrom two separate gas supplies.

2. Description of the Prior Art

There is a known device for controlling the gas mixture of differentkinds of gases in which each gas is expanded separately through atwo-stage pressure reducer to a uniform pressure and then each gas isdischarged through a respective adjustable metering nozzle controllingthe proportion in the gas mixture into the mixer tube. In order toobtain a uniform final pressure after the pressure reducers, thepressure reducers are provided with an auxiliary control which receivescontrol impulses from the uniform final pressure. The uniform finalpressure may be maintained by means of an equalizing controller whichacts on the control pressure of the pressure reducers. This has theeffect that upon occurrence of a pressure difference in the gas linesbetween the pressure reducers and the metering nozzles at the side ofthe higher pressure, the control pressure drops and a smaller gas volumeis delivered. At the other side the control pressure of the otherpressure reducer increases so that a larger volume of gas is delivered.In this manner, an equalized low pressure is produced which is a supplycondition for the metering nozzles. This known device has thedisadvantage that even at an equalized supply pressure, the rate of flowthrough the metering nozzles depends on the pressure in the mixing tube.In addition the unequal inside diameters of the nozzles must beconsidered. In this respect the rate of flow depends on the pressureratio. Thus the rate of flow and therefore the proportion of the mixturedepends on two factors which are not easily controllable. Consequentlysuch a device is unsuitable for apparatus in which the pressuredifferences can occur in the mixer tube. This disadvantage is ofimportance particularly in medical devices where for example ifnarcotics are admixed to a breathing gas there is a need for an exactproportion to be observed.

In another known method of mixing two gases in a predeterminedproportion, the gases to be mixed are supplied through pressuregovernors which for adjusting the pressure ratio are coupled to eachother. The outlet pressures of the pressure governors are arranged in anadjustable predetermined ratio to each other. Each gas flows at its ownpressure into a respective chamber having a predetermined or adjustablevolume. After the filling and interruption of the gas supply by a switchover valve, the gas flows into the gas outlet line through a furtherpair of pressure governors which are adjusted to the same pressure ratioas the first pressure governors. With such a method a gas mixture isproduced which has a definite concentration since a definite gasquantity is measured off each gas to be mixed. These quantities afterdischarge mix with each other in accordance with the meteredquantitative proportion. Concentration variations do not occur, not evenat variations of the gas pressure in the connected operated device. Toobtain this result however a relatively complicated arrangement isnecessary, primarily because of the requirement for two pairs ofpressure governors.

SUMMARY OF THE INVENTION

The present invention provides a method in a device of simple designwhich makes it possible to vary the mixing proportions of two gases toany desired extent with the aid of simple means and preferably with theuse of an electric control signal. In addition the device has to switchautomatically normal operating conditions to conditions which are safefor the user and at the same time it must signal such a disturbance.

In accordance with the invention a method is provided in which a firstgas such as a gas A controlled by a first control valve which opens at apredetermined initial pressure P₁ and closes at a predeterminedactuating pressure P₂ is admixed with a second gas. The second gas a gasB controlled by a second control valve which opens at an actuatingpressure P₂ and closes at a predetermined final pressure P₃ is suppliedto a pressure vessel along with the first gas and the gas mixture afterhaving reached the final pressure P₃ is discharged from the vesselthrough a third control valve which opens at a final pressure P₃ andcloses upon reestablishment of the initial pressure P₁.

The advantages obtained with the apparatus and method include the factthat only a single parameter that is the respective actuating pressureP₂ has to be varied in order to produce the desired gas mixture. In viewof the fact that the pressure meters which are available commerciallyare very accurate it is easy to provide for a control based entirely onpressure changes. The mixing of the gases is effected merely by varyingthe actuating pressure for opening and closing the various valves whichare necessary. The value of this actuating pressure P₂ which isintermediate two definite pressures that is an initial pressure P₁ and afinal pressure P₃ is a determining pressure for the proportion of gasesA and B in a mixture in accordance with the equation P₂ = P₁ + (P₃ -P₁)× A% divided by 100; where A is the desired proportion of gas A andthe proportion of gas B in the mixture is B%= 100 %-A%.

Since after the first adjustment P₁ and P₃ are constant thedetermination of the actuating pressure P₂ is very simple. A gas mixingapparatus in accordance with the present method would be equipped with acorresponding ranging adjusting device.

A gas mixing device for carrying out the inventive method is very simplein design and since only a single pressure is to be varied for varyingthe gas proportion in the mixed gas, is free from problems of operation.For conveying the gases in the gas mixing device, only a few componentparts are needed which form an operational unit insofar as the supplylines for the gases A and B are concerned. The construction includes afirst and second supply line connected into a pressure vessel eachhaving its associated first and second control valve and a delivery linewhich extends outwardly from the pressure vessel for supplying the mixedgas which has its own control valve. In addition a supply reservoir maybe connected to the mixed gas line.

The control valves are advantageously designed as solenoid valves whichare coupled through a pneumatic electrotransducer to a pressure meterprovided on the pressure vessel. The first control valve in the firstgas supply line is advantageously adjusted for opening to an initialpressure P₁ and for closing it operates at an actuating pressure P₂. Thesecond control valve and the second gas supply line is adjusted forexample to open to an actuating pressure P₂ and to close at a finalpressure P₃. The third control valve is adjusted for opening at a finalpressure P₃ and for closing the initial pressure P₁.

Particular advantages of the invention result from the possibility ofequipping the control valve with a control device which starts with theopening of the second control valve and is stopped with the closing and,upon exceeding the normal time up to the closure, releases a switchpulse and starts an alarm. This would make it possible to use the gasmixing device in breathing apparatus and medical devices. For suchapparatus and devices it is essential that any undesirable operationalconditions will not lead to dangerous consequences to the patient. Forexample in the medical technique preferably compressed air is mixed withoxygen and laughing gas is mixed with oxygen. While air is mixed withoxygen upon a supply interruption of one of these gases the other gashas to continue to flow to the patient. However not only the cases to beconsidered in which as just mentioned both gases are breathable but alsothe possibility that one of the gases is breathable and the other gasmay be even dangerous. In the first case thus with a breathable gas bothcontrol valves for gases A and B are equipped with a control device bywhich upon interruption of the supply of one of the gases the controlvalve of the other gas is automatically switched to the entire pressurerange from P₁ to P₃ so that then during the whole filling phase thesingle gas will be continued to be supplied to the pressure vessel.

In contrast thereto if one of the gases is breathable and the other isnot, the control valve is equipped with control device for thenon-breathable gas. Such a control device would effect a switching ofthe breathable gas to the full operation in the event of disruption ofthe non-breathable gas but it would switch off the device in the eventof the cutout of the breathable gas so that the non-breathable gas wouldnot be supplied alone. Simultaneously at the occurrence of thiscondition an alarm is started and this is of vital importance.

In another embodiment of the invention the pressure vessel may beconnected to a switch-over valve which permits either inflow of themixed gas into the pressure vessel or the outflow of the mixed gas to amixed gas supply line. In addition the two supply lines for the gas maybe connected through a switch-over valve to a single supply line to thepressure vessel which is connected to the first switch-over valve.

Accordingly it is an object of the invention to provide a method for thecontrol of the proportion of two gases which are delivered to a mixedgas line from a pressure control vessel which comprises continuouslymonitoring the pressure in the control vessel and when the pressuretherein is at an initial predetermined pressure admitting a first gasinto the pressure control vessel until the pressure in the vesselincreases to a predetermined higher pressure and then stopping theadmission of the first gas and initiating the admission of a second gasinto the pressure control vessel, continuing to admit the second gasuntil a predetermined additional higher pressure is reached and thenstopping the admission of the second gas and beginning the withdrawal ofthe mixed gases from the pressure vessel to the mixed gas line, andcontinuing to withdraw the mixed gases until the pressure in thepressure vessel returns to the initial predetermined pressure andrepeating the procedure.

A further object of the invention is to provide an apparatus for mixingtwo gases in a predetermined proportion which comprises a pressurecontrol vessel with a first connecting line for the supply of a firstgas having a first valve therein and a second connecting line for asupply of a second gas having a second control valve therein and with athird mixed gas control valve in a mixed gas line connected to thepressure control vessel wherein each of the first, second and thirdvalves are set to operate for opening and closing at distinct differentpressures and which includes a transducer connected to the pressurevessel to monitor the pressure and to effect the pressure controlopening and closing of the first, second and third valves in accordancewith their set values of pressure for opening and closing.

A further object of the invention is to provide a device for mixing twogases in a predetermined portion which is simple in design, rugged inconstruction and economical to manufacture.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference should be had to the accompanying drawing and descriptivematter in which there are illustrated preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

FIG. 1 is a diagrammatical view of a gas mixing device constructed inaccordance with the invention; and

FIG. 2 is a view similar to FIG. 1 of another embodiment of theinvention.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in particular the invention embodied thereinin FIG. 1 comprises an apparatus for mixing two gases in a predeterminedproportion and it includes a gas supply line 1 for a first gas A and agas supply line 2 for a second gas B which are connected through a firstcontrol valve 3 and a second control valve 4 respectively to a pressurevessel 5. The pressure in the pressure vessel 5 is measured by a meter 6and variations of pressure are employed for producing a control of eachof the second valve 3 and 4 and a third discharge valve 7 in a mixed gasline 8 and using a control device such as a transducer 15. The mixed gasline 8 may be connected for supplying the mixed gas directly to itsplace of use or it may be delivered to a supply reservoir 9 as indicatedin FIG. 1.

An example of the operation of the device is as follows.

An initial pressure in the vessel 5 may be said for example to be apressure P₁ of two bars. Under this pressure the control device 15actuates-the first control valve 1 so that it opens. The first gas Athen flows through the supply line 1 into the pressure vessel 5. The gasA continues to flow into the pressure vessel 5 until the pressure in thevessel increases to an actuating pressure P₂ which is a predeterminedpressure which may for example be 2.7 bars. This actuating pressure P₂acts through the control device 15 to close the first control valve 3and to open the second control valve 4. The first gas A stops flowingand the gas B then flows in through the supply line 2 and the controlvalve 4 into the pressure vessel 5. This causes the pressure in thepressure vessel 5 to increase until a predetermined additional pressurea pressure P₃ is reached which for example may be 3 bars. At theadditional pressure value the second control valve 4 will be closed bythe control mechanism 15 and a third control valve 7 will be opened atthis additional pressure P₃. Therefore the mixed gas will flow out ofthe pressure vessel 5 through the third control valve and either intothe supply reservoir 9 or directly through the mixed gas line 8 to theplace of use. With this discharge the pressure in the pressure vessel 5will decrease again until it arrives at the initial pressure P₁.Thereupon the third control valve 7 is set to be closed by the control15 and the first control valve 3 will be reopened. At this stage thenext cycle is started and then repeated.

The proportion of gases A and B in the mixed gas follows the actuatingpressure P₂. In the present example, the mixed gas contains 70% of gas Aand 30% of gas B. These percentages result from the adjusted actuatingpressure P₂ = 2.7 bars, the initial pressure P₁ = 2 bars and the finalpressure P₃ = 3 bars.

Since P₂ can be varied within the range of P₁ to P₃ the proportion ofthe gases can be adjusted from zero to 100% of the mixed gas.

The embodiment of the invention shown in FIG. 2 is similar to that ofFIG. 1 and similar parts are similarly designated but with a prime. Inthis embodiment the control valves which are employed include a singleswitch-over valve 11 which is connected through a line 10 to thepressure vessel 5' and a line 10a to the selected connection of thesupply connections 1' and 2'. In addition the switch valve 11 is alsoconnected to a mixed gas line or supply 8'. The valve 12 permits aswitch-over from the supply lines 1' or 2' for the gases A and B to feedone or the other through the connecting line 10a to the switch valve 11.

In the embodiment of FIG. 2 at an initial pressure P₁ gas A flows to thepressure vessel 5 to the switch-over valve 12 which is switched to thesupply line 1 and through a switch-over valve 11 which is switched tothe inlet 13 connecting the connecting line 10a. When the pressure P₂ isreached in the vessel 5' the switch-over valve 12 is operated to theposition in which gas B from the supply line 2 can flow through theconnecting line 10a in the switch-over valve 11 remains in an unchangedposition so that the gas B can flow into the pressure vessel 5'. As soonas the pressure P₃ is attained the switch-over valve 11 switched to theoutlet 14 leading to the mixed gas line 8'. The mixed gas is thendischarged. Thereupon the pressure is reduced to an initial pressure P₁,the switch-over valve 11 switches again to the inlet 13 and switch-overvalve 12 switches to supply line 1 and thereby to gas A.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

Each of the circuits connected to the first control valve 3 and thesecond control valve 4 in the embodiment of FIG. 1 is advantageouslyprovided with an alarm device R which becomes actuated when either ofthe valves 3 or 4 fail to switch when a given pressure condition iseffected in the pressure vessel.

What is claimed is:
 1. A method of controlling the proportion of twogases which are delivered to a mixed gas line from a pressure controlvessel, comprising continuously monitoring the pressure in the controlvessel and when the pressure therein is at an initial predeterminedpressure admitting a first gas into the pressure control vessel untilthe pressure in the vessel increases to a predetermined higher pressureand then stopping the admission of the first gas and initiating theadmission of a second gas into the pressure control vessel, continuingto admit the second gas until a predetermined additional higher pressureis reached at which the admission of the second gas is stopped and themixed gas is withdrawn through the mixed gas line continuing to withdrawthe mixed gas through the mixed gas line until the pressure in thepressure control vessel reduces to the initial pressure and stopping thewithdrawal at the reaching of the initial pressure and initiating onceagain the admitting of the first gas into the pressure control vesseland repeating the process.
 2. A method according to claim 1, wherein thewithdrawn mixed gases are delivered directly to a user.
 3. A methodaccording to claim 1, wherein withdrawn mixed gases are directed into asupply reservoir.